The game starts with a series of missiles descending from the top of the screen. The mouse cursor becomes a targeting sight and the player must position it in the path of the oncoming missiles and click a mouse button to trigger an explosion which destroys said missile. As the player progresses the missiles fall faster and become more numerous.
The object of the game is to defend the cities at the bottom of the screen as long as possible. The longer the game is played and the more missiles that are destroyed the higher the score.